1. Field of the Invention
This invention relates generally to gas mass flow control systems and, specifically, to one having a high turndown regulation means for controlling the gas mass flow to a variable pressure system.
2. Discussion of the Relevant Art
Current gas flow control systems which regulate gaseous fuel flow to a variable pressure system, such as a combustion engine, attempt to regulate pressure first, and then, fuel flow control. Illustrative of relevant gas fuel flow control systems are those disclosed in U.S. Pat. No. 4,146,051, issued to Sparks, and U.S. Pat. No. 4,796,651 issued to Ginn et al. Sparks employs, in a gas flow control system, a variable metering device, a circuit for generating a first electrical signal which is a function of a desired gas flow through the metering device, a circuit for generating a second electrical signal which is a function of the gas pressure upstream of the metering device, and control means which is responsive to the first and second electrical signals, for varying the effective flow area of the metering device. Of notable distinction in the Sparks patent is the teaching of the variable metering device which, in addition to serving as a restriction in the system fuel flow, also physically effects variability in the flow. Ginn et al. teach a method and apparatus for measuring gas flow volume in a system which references the total pressure upstream of a bypass orifice in order to produce a first signal representative of the differential pressure between the total pressure upstream and of the orifice and the static pressure downstream of the orifice. The first and a second signal, which is related to the area of the opening in the orifice, are supplied to a gas flow volume data base which is then correlated to the sensors and to the orifice in the duct. The control means of the system references a library or lookup table and divulges the gas flow volume (not mass) occurring in the duct. Thus, current systems do not control the flow of gas (by mass rate flow) into a load system where the gas delivery pressure at the load varies directly as a function of the mass flow.